There are two principal purposes for the present research. One will be to gather and integrate information on the effects of gonadal steroids on several behaviors in rodents, focusing on the behaviors which affect body weight and composition. The second goal of the project will be to study some of the molecular mechanisms by which sex hormones affect neural and nonneural target tissues to alter behavior. A great deal of previous work indicates that gonadal hormones have important effects on behavioral regulation of body weight in a wide range of mammalian species, ranging from rodents to primates. Work in rodents suggests that the regulated body weight (set-point) is determined, in part, by circulating levels of sex steroids. Specific projects will focus on sites and pathways of action in brain and peripheral tissues, with some work on species differences. Molecular endocrinologists have provided a great deal of information on the subcellular mechanisms of steroid action. The second portion of this project will use some of their techniques to study steroid effects on behavior. Specific projects will attempt to correlate binding of sex hormones in target tissues with effects on sexual behaviors and regulatory behaviors.